Rotating Tungsten Helium cooled Target RoTHeTa Cyril Kharoua Daniela Ene, Ferenc Mezei, Etam Noah, François Plewinski, Pascal Sabbagh, Luca Massidda (CRS4, Sardinia) Peter Sievers (retired from CERN) Fernando Sordo (ESS-Bilbao) 4 th High Power Targetry Workshop Malmö

Outline  Some history  Practical motivation for Helium cooling  Practical motivation for Granular Target  Practical motivation for Rotating Target  Main parameters of the RoTHeTa  Neutronic performance  Thermo-Mechanical study  Loop characteristics  Rotating seal  Maintenance  Lifetime  Conclusion

Page 3 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Some history  Granular Tungsten target helium cooled was first proposed by Peter Sievers for a MW neutrino factory  First we have considered spheres in a stationary target  Optimum configuration for cooling, thermal shock and thermal stress  Heavy cooling requirements (High Pressure!) Under the ESS condition a rotating wheel, fitted with tungsten rods and cooled with helium is a viable solution…

Page 4 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Practical Motivation for Helium Cooling  Objectives: Avoid Liquid metal technology Avoid Water cooling / corrosion issue related to tungsten target and therefore avoid cladding  Advantages: Known technology Low activity in the cooling fluid Leak tightness  Drawbacks: Pressurized gas equipment (3-10bar) Leak tightness

Page 5 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Practical Motivation for Granular Target  Objectives: Allows cooling fluid to remove heat within the target (directly where it is deposited)  Advantages: High density target (75% to 90% of pure tungsten) No thermal shock and low stress level Flexible target material (choice, arrangement, geometry…)

Page 6 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Practical Motivation for a Rotating Target  Objectives: Increase lifetime (window, tungsten…) Alleviate the heat removal  Advantages: Dilution of specific activity and after heat Less frequent maintenance and handling of radioactive material Solid waste Upgradeable for higher beam power  Drawbacks: Not yet proven concept (but we do not need to re-invent the wheel!) Rotating seals to be adapted from existing solutions Heavy assembly

Page 7 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Main Parameters of the Helium Cooled Rotating Granular Target  A 2.5GeV elliptic Gaussian beam with an RMS of  x = 5 cm and  y = 1.5 cm (beam footprint at 4  of 20cm x 6cm), an average power of 5 MW, pulsed at 20 Hz  The wheel is rotating at 30RPM (0.5Hz)  The energy deposition calculated with FLUKA gave a maximum Power density (time average for 1/40 of the wheel) of 75W/cm 3 (40 times less than in the static target case).  External wheel diameter is150 cm and internal diameter of 50 cm. The helium is blown over the total surface continuously.  Initially rods of 2cm diameter, now 1cm diameter

Page 8 Cyril Kharoua – 4 th HPTW – Malmö – May Brightness at 5 MeV (left) and at 10 MeV (right) on the moderator surface for a 1ms pulse length. Neutronic performance The rotating target made of rod cooled by helium will allow a density of 90% of the raw material, which shall give a performance close to the pure tungsten configuration. courtesy F. Sordo et al.

Page 9 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Neutronic performance  Franz Gallmeier investigation (previous TSCS meeting) extended Rotating target configuration (run though optimization loop) Extrapolation with density (not so accurate) Tungsten is the most favourable target material, and its dilution is not affecting significantly the neutron production Element Effective density Φ Comment (1/cm 3 )(n/cm 2 /prot.) Perf in % vs. Best Loss in % vs. Best W E %0.00%Calculated Sphere pure W145.66E %9.93%Calculated Sphere Densimet (*) E %10.74%Educated guess Rods Densimet (*) E %3.53%Educated guess *DENSIMET is a tungsten alloy with appropriate properties courtesy F. Gallmeier

Page 10 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Thermo-mechanical study 2cm Rods With a He-cooling circuit set at: Po = 10 Bar, v(He) 8 m.s - 1 (mass flow of about 20kg/s!!! Which could reduced by tuning it for different zones) The peak temperature in the hottest rods is about 577°C (Inlet Temperature was 200°C) Helium ∆T bulk =30K Stress in the rods is low even in a fatigue regime (endurance), about 30 to 50 MPa

Page 11 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Thermo-mechanical study He in inlet is at 200°C and exit at about 230°C Pressure drop is about 0.2bar and Pumping power about 250kW Helium Inlet Helium Outlet Rotation axis

Page 12 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Thermo-mechanical study 1cm Rods With a more moderate He-cooling circuit (Po = 3 Bar, inlet v(He) of 4 m.s-1, mass flow of 3kg/s) The peak temperature in the hottest rods is about 485°C Helium ∆T bulk = 200K Stress in the rods is very low even in a fatigue regime (endurance), about 10 to 20 Mpa

Page 13 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 For 3kg/s mass flow rate for 3 bar He Here the pressure drop is 0.1bar equivalent to 62kW of pumping power. Thermo-mechanical study 1cm Rods

Page 14 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Cross flow configuration 14 H2H2 No contact labyrinth (Pump outside) He:  0.3 m 3,  10 bar He:  5 m 3, > 1 bar H2OH2O W Containment with flange connection of target trolley & utilities p

Page 15 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Thermo-mechanical study Cross flow configuration 15  Transverse cross flow is under estimation  The objective is to use a lower mass flow rates and increase the bulk ∆T in Helium  First estimation show the possibility to consider 2cm rods with 1mm gap (82%of the full W density). Mass flow rates is about 3kg/s ∆T bulk =200K T max in He =310°C ∆P≈1bar (VDI WärmeAtlas)

Page 16 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Helium loop Pressure drop estimation  The main component of the loop to be considered for the overall pressure head required at the pump are: The target material (see previous slides) The target shaft and other straight pipe (Half of the target) The Inlet rotating seals and outlet rotating seals The filters (Half of the target) The heat exchanger (Half of the target)  The Inlet and Outlet rotating seals could be assumed to have the same pressure drop  The Heat exchanger could be assumed to have half of the pressure drop seen in the target material

Page 17 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Helium loop Pressure drop estimation Pressure drop [bar] The target material 0.1 The target shaft and other straight pipe 0.05 The Inlet rotating seals 0.1 The outlet rotating seals 0.1 The filters 0.05 The heat exchanger Total Pumping Power kW Preliminary estimation A preliminary assessment could give indication of the pressure drop in the main component of the loop, for Helium flowing at 3kg/s and 3bar for a global volume of 2m 3

Page 18 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Helium Loop and ancillaries loop

Page 19 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Leak in Rotating Seals  Differential pumping seal with chicanes between 3 bar and atmospheric pressure.  For 0.1mm wide and 50cm long path => at most 2g/s Pumping of the leak occurs in the last chicane

Page 20 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Structural analysis  Structural analysis Simplified shell model (sector) Parameterized model (number of ribs, thickness) No thermal loads defined, but gravity, pressure (3bar), rotational velocity Simplified post-processing using RCC-MRx criteria

Page 21 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Structural analysis  The table here summarize the ratio between the acceptable limit (according to RCC-MRx criteria) and the calculated stress.  At 3bar with ribs every 12degree, the minimum thickness of material could be 3mm.  If the pressure can be further reduced, the number of needed ribs (or shell thickness) will be reduced Angle between 2 ribs Thickness (mm)

Page 22 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Maintenance / Layout

Page 23 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Maintenance / Layout

Page 24 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Maintenance / Layout  Exchange procedure: a proposal  Hot cell could be separated from the target station / monolith allowing an operation of it more disconnected from the target operation  In order to reduce the weight carried by the overhead crane the flask is moved on rails  Basic maintenance is performed on helium circuit (rotating seal, filters, pumps, heat exchanger) by hands on it. The exposure to radiation shall be low.

Page 25 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Lifetime  The lifetime of such target is supposed to be about 40 times longer than the static target As radiation damage will be spread over a large surface/volume Fatigue is negligible in the first estimation (non irradiated)

Page 26 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Conclusion  3bar of pressure seems a viable option with 1cm rods, but further study shall be carried on to confirm and determine the minimum pressure acceptable  Neutron yield is optimum  Some of the main challenges lie in the replacement of the target and its associated downtime  Attention has to be paid to local leak and radioactive release  Special attention has to be paid to the rotating seal

Page 27 Cyril Kharoua – 4 th HPTW – Malmö – May 2011 Thank you for your attention